You can just add a second line to /etc/passwd with a different username but the same numerical uid. Like this:

    altroot:x:0:0:Alternative Root User:/:/bin/sh

Then, of course, run (as root) "passwd altroot" to set a password.

We used to do this all the time for users who needed root access to their own workstation. It allowed us to avoid telling them the common root password used on all the machines in the organization.

In your case, doing this might be beneficial in case there is a network problem because you'll have a way to log in as root locally.